Aluminum alloy

ABSTRACT

All aluminum alloy is disclosed that includes 6.5 to 8.5 percent silicon, 0.6 to 1.0 percent iron, 0.0 to 0.5 percent manganese, 0.35 to 0.65 percent magnesium, 0.0 to 1.0 percent zinc, 0.0 to 0.2 percent titanium, 2.0 to 2.5 percent copper, and aluminum as the remainder with further one or more other elements that are 0.0 to 0.15 percent of the weight of the aluminum alloy. An aluminum alloy of the above composition is high in strength and suitable for use with SSM methods of casting, such as Rheocasting and Thixocasting.

FIELD OF THE INVENTION

[0001] The present invention relates generally to casting alloys. Moreparticularly, the present invention is directed to an aluminum alloy forsemi-solid metal (SSM) casting processes.

BACKGROUND OF THE INVENTION

[0002] SSM aluminum alloy castings outperform, in both cost andperformance, other casting techniques, such as conventional die casting,which is performed under high pressure, gravity permanent mold castingand squeeze casting. SSM casting methods, when utilized for themanufacturing of aluminum alloy products/castings, have provenadvantageous over other casting techniques because SSM castings tend toexhibit higher mechanical properties in the areas of strength andductility and reduced porosity than castings produced by theabove-listed other methods.

[0003] Microstructures of SSM aluminum alloy castings reveal the primaryphase particles as round crystals that are often referred to as rosettesor globules. The primary phase particles in SSM aluminum alloy castingsthat contain less than twelve percent silicon are comprised ofessentially aluminum. Because solid primary phase particles are part ofthe semi-solid metal being injected into a mold/die cavity, themicrostructure of the primary phase of an aluminum alloy prior toinjection into a mold/die is indicative of the microstructure of theprimary phase of the resulting aluminum alloy casting. Thus, when SSMmethods of casting are utilized, the mechanical properties of a castingcan be predicted before a casting is even produced. Accordingly, theproduction of castings with defects can be avoided.

[0004] Unlike SSM methods of casting, non-SSM casting processes involveinjection/pouring of a molten metal directly into the die. Thus, becausethe metal is molten, with no parts of the metal being solid, themicrostructure of the resulting casting cannot be ascertained untilafter the molten metal has solidified in the mold/die cavity. Thus, withnon-SSM casting processes the microstructure of the primary phase of acasting cannot be predicted before the casting is formed.

[0005] Typically, the microstructures of castings prepared by non-SSMcasting processes have dendrites. Dendrites are “tree-like” structures,and castings with dendrites are prone to microporosity and have inferiormechanical properties than those that exhibit round crystals.

[0006] Thixocasting and Rheocasting are SSM methods of casting.Thixocasting involves the electromagnetic stirring of metal duringsolidification/freezing to provide aluminum SSM feedstock billets up toapproximately 4″ in diameter. The stirring action due to the movement ofliquid fragments the aluminum dendrites as they form duringsolidification and results in the formation of small equiaxed grains inthe billets. The billets are subsequently cut into slugs, and re-heatedto a semi-solid state before being injected into the cavity. It isduring the billet re-heating stage that the equiaxed aluminum grainsundergo globularization. Chemically grain-refined billets are often usedin lieu of electromagnetically stirred billets. Heating of grain-refinedbillets in the semi-solid temperature regime also helps yield globularprimary phase particles prior to injection into die cavity.

[0007] Rheocasting, which is also known as “slurry” or“slurry-on-demand” casting, involves heating a metal to a liquid state,cooling the molten metal to a semi-solid state, and then injecting thesemi-solid metal into the die cavity. Rheocasting is more efficient thanThixocasting because Rheocasting involves fewer steps than Thixocasting.

[0008] Rheocasting has also proven to be more economically feasible thanThixocasting because any unused scrap metal can be easily re-melted andreprocessed by an SSM component manufacturer. With Thixocasting, thescrap metal has to be reformed into billets by the billet manufacturervia the use of electromagnetic stirring or chemical grain refiningbefore being used again. However, unlike Thixocasting, Rheocastingrequires only that the scrap metal is re-melted and cooled to asemi-solid state before it is injected into a die cavity. As a result,scrap metal can easily be reused with the Rheocasting method of SSMcasting and the expense associated with recycling scrap metal is less.

[0009] In recent years, SSM casting methods utilizing aluminum alloyshave been used for manufacturing brake cylinders, fuel rails, enginebrackets steering knuckles, suspension links and auto seat backsbecause, in addition to the above-discussed advantages over non-SSMcasting techniques, SSM casting methods offer non-turbulent filling(i.e., less air entrapment), require lower die temperatures, reducecycle time, reduce shrinkage, and provide the option of heat treatment(i.e., solution treatment).

[0010] Among the various casting alloys in use, A356.2 and 357 are theprimary aluminum alloys used for SSM castings, including castings ofautomotive components. The chemistries of A356.2 and 357 are as follows:A356.2 357 Percent of Percent of Element Weight Element Weight Silicon6.5-7.5 Silicon 6.5-7.5 Iron 0.12 max Iron 0.12 max Manganese 0.05 maxManganese 0.03 max Magnesium 0.30-0.45 Magnesium 0.45-0.6 Zinc 0.50 maxZinc 0.05 max Titanium 0.20 max Titanium 0.20 max Copper 0.10 max Copper0.03 max Others 0.15 total Others 0.15 total Aluminum Balance AluminumBalance

[0011] A356.2 and 357, when used with SSM casting methods, generatecastings of essentially high toughness, i.e., ability to absorb energybefore failure, and thus, have been found suitable for automotivecomponents, such as steering knuckles and suspension links.

[0012] However, the A356.2 and 357 alloys, when used with SSM castingmethods, have not been found suitable for automotive components thatrequire essentially high strength, i.e., high load bearing ability, suchas axle carriers, rack and pinion housings, and steering columnhousings.

[0013] There are, however, problems associated with the use of A356.2and 357 aluminum alloys. Maintaining low percentages of iron, copper andzinc increases the cost of the A356.2 and 357 aluminum alloys. Bykeeping the iron content low, there is also the potential that solderingwill occur during the casting process. Soldering refers to thephenomenon that takes place when aluminum adheres to the die cavityduring the die casting process. Soldering occurrences often lead todefective castings.

[0014] Accordingly, it is desirable to provide an aluminum alloy thatcan be utilized with SSM methods of castings, especially with theincreasingly popular Rheocasting method of SSM casting, that can producehigh integrity, high-strength automotive components, such as axlecarriers, rack and pinion housings, and steering column housings.

[0015] Further, it is desirable to provide an aluminum alloy that isless prone to the soldering phenomenon.

[0016] It is also desirable to provide an alloy that is less expensiveto produce than other alloys such as A 356.2 and 357.

SUMMARY OF THE INVENTION

[0017] In an exemplary embodiment of the present invention, an alloy inaccordance with the present invention is provided that includes 6.5 to8.5 percent silicon, 0.60 to 1.0 percent iron, 0.0 to 0.5 percentmanganese, 0.35 to 0.65 percent magnesium, 0.0 to 1.0 percent of zinc,0.0 to 0.2 percent titanium, 2.0 to 2.5 percent copper, and aluminum asthe remainder with further one or more other elements 0.0 to 0.15percent of the weight.

[0018] In another exemplary embodiment of the present invention a diecast product is provided that includes 6.5 to 8.5 percent silicon, 0.60to 1.0 percent iron, 0.0 to 0.5 percent manganese, 0.35 to 0.65 percentmagnesium, 0.0 to 1.0 percent of zinc, 0.0 to 0.2 percent titanium, 2.0to 2.5 percent copper, and aluminum as the remainder with further one ormore other elements 0.0 to 0.15 percent of the weight.

[0019] In yet another exemplary embodiment of the present invention amethod of making a die cast product is provided that includes forming asemi-solid aluminum alloy, wherein the semi-solid aluminum alloycontains 6.5 to 8.5 percent silicon, 0.60 to 1.0 percent iron, 0.0 to0.5 percent manganese, 0.35 to 0.65 percent magnesium, 0.0 to 1.0percent of zinc, 0.0 to 0.2 percent titanium, 2.0 to 2.5 percent copper,and aluminum as the remainder with further one or more other elements0.0 to 0.15 percent of the weight, and placing the semi-solid aluminumalloy in a die cavity.

[0020] There has thus been outlined, rather broadly, the more importantfeatures of the invention in order that the detailed description thereofthat follows may be better understood, and in order that the presentcontribution to the art may be better appreciated. There are, of course,additional features of the invention that will be described below andwhich will form the subject matter of the claims appended hereto.

[0021] In this respect, before explaining at least one embodiment of theinvention in detail, it is to be understood that the invention is notlimited in its application to the details of construction and to thearrangements of the components set forth in the following description orillustrated in the drawings. The invention is capable of otherembodiments and of being practiced and carried out in various ways.Also, it is to be understood that the phraseology and terminologyemployed herein, as well as the abstract, are for the purpose ofdescription and should not be regarded as limiting.

[0022] As such, those skilled in the art will appreciate that theconception upon which this disclosure is based may readily be utilizedas a basis for the designing of other structures, methods and systemsfor carrying out the several purposes of the present invention. It isimportant, therefore, that the claims be regarded as including suchequivalent constructions insofar as they do not depart from the spiritand scope of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023]FIG. 1 illustrates microstructures of an exemplary embodiment analuminum alloy in accordance with the present invention.

[0024]FIG. 2 illustrates microstructures of an exemplary embodiment ofan aluminum alloy in accordance with the present invention.

[0025]FIG. 3 illustrates microstructures of an exemplary embodiment ofan aluminum alloy in accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

[0026] An aluminum alloy in accordance with the present invention is ahigh copper, manganese and iron (HiCMF) aluminum alloy. In an exemplaryembodiment of the present invention, an aluminum alloy in accordancewith the present invention, is composed of the below-listed elements, bypercentage of weight, as follows: Element % of Weight Silicon 6.5 to 8.5Iron 0.6 to 1.0 Manganese   0 to 0.5 Magnesium 0.35 to 0.65 Zinc   0-1.0Titanium   0-0.2 Copper 2.0-2.5 Tin   0-0.3 Others   0-0.15 AluminumBalance

[0027] In a preferred embodiment of the present invention, the “others”are lead and/or chromium.

[0028] An aluminum alloy in accordance with the present invention issuitable for SSM methods of casting because the microstructure of theprimary aluminum phase of the metal slurry prior to its injection into adie cavity is comprised of globular and/or rosette crystals.

[0029] An alloy in accordance with the present invention is hypoeutecticbecause its silicon content is less than 12 percent. The primary phasemetal of an alloy in accordance with the present invention is aluminum.

[0030] Alloys with silicon composing less than twelve percent of theirweight are hypoeutectic and alloys with silicon composing more thantwelve percent of their weight are hypereutectic.

[0031] Referring to FIG. 1 and FIG. 2, shown are microstructures of theprimary phase from various locations of an aluminum alloy in accordancewith the present invention prior to its injection into a die cavity. Theillustrations of FIG. 1 and FIG. 2 were ascertained in accordance withthe conventional evaluation method of “water-quenching,” which “locksin” the microstructure. The microstructures of FIG. 1, from top tobottom, are from the middle edge 10, middle 12 and center 14 of awater-quenched slug. It can be seen from FIG. 1 that the primaryaluminum phase particles consist of round crystal/globular 16, and/orrosette 18 formations.

[0032]FIG. 2 depicts microstructures of the primary phase of an aluminumalloy in accordance with the present invention prior to its injectioninto a die cavity. The microstructures of FIG. 2, from top to bottom,are from the bottom edge 20, middle 22 and center 24 of a water-quenchedslug. It can be seen from FIG. 2 that the primary aluminum phaseparticles of an aluminum alloy in accordance with the present inventionconsist of round crystal/globular 26 and/or rosette 28 formations.

[0033]FIG. 3 depicts microstructures of the primary phase of an aluminumalloy in accordance with the present invention after it has beeninjected into a die cavity. It can be seen from FIG. 3 that the primaryaluminum phase particles of an aluminum alloy in accordance with thepresent invention consist of round crystals/globular 32 and/or rosette34 formations. Thus, when FIG. 1 and FIG. 2 are compared with FIG. 3, itcan be seen that the morphology of the primary aluminum phase prior toinjection into a die cavity is similar to that of the aluminum alloy inthe resulting casting. Accordingly, the microstructure of the primaryphase of an alloy in accordance with the present invention can bedetermined before it is utilized to form a casting. Thus, the number ofcasts with microstructures unsuitable for their purpose can be reduced.

[0034] In an exemplary embodiment of the present invention silicon isrestricted to 7.2 percent to 8 percent of the weight to efficientlyachieve formation of the primary aluminum phase during the cooling ofthe molten metal to the semi-solid state.

[0035] Additionally, the amount of silicon present in an aluminum alloymay be directly related to the strength of the aluminum alloy.Typically, the higher the content of silicon, the higher the strength ofthe aluminum alloy. In exemplary embodiments of the present invention,the average silicon content of the alloy is higher than other alloys,such as the A356.2 and 357 aluminum alloys. Accordingly, the strength ofan aluminum alloy in accordance with the present invention is higherthan other alloys, such as A 3562.2 and 357.

[0036] Further, as shown in FIG. 3, an aluminum alloy in accordance withthe present invention reveals the presence of fine aluminum-siliconeutectic and entrapped intermetallic particles 30 within the roundcrystals, globular and/or rosette primary aluminum phase. The entrappedintermetallic particles 30 essentially consist of iron, silicon andmanganese.

[0037] Typically, the formation of the intermetallic particles 30, suchas those shown in FIG. 3, lead to fractures that travel along a path(fracture path) within the structure of the casting. However, becausethe intermetallic particles 30 are entrapped within the roundcrystal/globular 32 and/or rosette 34 structures, the fracture path isnow restricted. Accordingly, fractures occur with less frequency,especially when an aluminum alloy in accordance with the presentinvention is compared to the A356.2 and 357 aluminum alloys that do notreveal entrapped particles in their microstructures in the primaryaluminum phase.

[0038] The formation of the intermetallic particles in an aluminum alloyin accordance with the present invention can be attributed to the highcontent of iron in the aluminum alloy. In an exemplary embodiment of thepresent invention, iron is 0.6 to 1.0 percent of the weight. In anotherexemplary embodiment of the present invention iron is 0.6 to 0.8 percentof the weight. The iron content of an aluminum alloy in accordance withthe present invention is higher than other alloys, such as A 356.2 and357 which are, at a maximum, 0.12 percent of the weight. Accordingly, analloy in accordance with the present invention is less expensive than A356.2 and 357 because the iron content does not have to be maintainedlow. Additionally, because the iron content is not low, the potential ofsoldering is reduced.

[0039] In an exemplary embodiment of the present invention, magnesium isapproximately 0.35 to 0.65 percent of the weight. The magnesium contentof an aluminum alloy in accordance with the present invention is higherthan the magnesium content of other aluminum alloys, such as the A 356.2and 357, which is 0.30 to 0.45 and 0.45 to 0.6 percent of the weight,respectively. The strength of a casting made from an aluminum alloy inaccordance with the present invention will be even greater after thealloy has been heat treated, i.e., subjected to a solution treatment andartificially aged. In a preferred embodiment of an aluminum alloy inaccordance with the present invention, the magnesium content isapproximately 0.45 to 0.6 percent of the weight.

[0040] As a result of its high strength, an aluminum alloy in accordancewith the present invention is suitable for the manufacturing of productsthat require high strength, such as axle carriers, rack and pinionhousings and steering column housings by both Rheocasting andThixocasting.

[0041] The many features and advantages of the invention are apparentfrom the detailed specification, and thus, it is intended by theappended claims to cover all such features and advantages of theinvention which fall within the true spirit and scope of the invention.Further, since numerous modifications and variations will readily occurto those skilled in the art, it is not desired to limit the invention tothe exact construction and operation illustrated and described, andaccordingly, all suitable modifications and equivalents may be resortedto as falling within the scope of the invention.

What is claimed is:
 1. An aluminum alloy, consisting essentially of thefollowing constituents by percentage of weight: 6.5 to 8.5 percentsilicon; 0.6 to 1.0 percent iron; 0.0 to 0.5 percent manganese; 0.35 to0.65 percent magnesium; 0.0 to 1.0 percent zinc; 0.0 to 0.2 percenttitanium; 2.0 to 2.5 percent copper;  0.0 to 0.15 percent one or moreother elements; and aluminum as the remainder.


2. The aluminum alloy of claim 1, wherein the aluminum alloy comprises7.2 to 8 percent silicon.
 3. The aluminum alloy of claim 1, wherein thealuminum alloy comprises to 0.6 to 0.8 percent iron.
 4. The aluminumalloy of claim 1, wherein the aluminum alloy comprises 0.45 to 0.6percent magnesium.
 5. The aluminum alloy of claim 1, wherein the one ormore other elements is lead.
 6. The aluminum alloy of claim 1, whereinthe one or more other elements is chromium.
 7. The aluminum alloy ofclaim 1, wherein the one or more other elements are lead and chromium.8. A die cast product, comprising by percentage of weight: 6.5 to 8.5percent silicon; 0.6 to 1.0 percent iron; 0.0 to 0.5 percent manganese;0.35 to 0.65 percent magnesium; 0.0 to 1.0 percent zinc; 0.0 to 0.2percent titanium; 2.0 to 2.5 percent copper;  0.0 to 0.15 percent one ormore other elements; and aluminum as the remainder.


9. The die cast product, of claim 8, wherein the die cast productcomprises 7.2 to 8 percent silicon.
 10. The die cast product of claim 8,wherein the die cast product comprises 0.6 to 0.8 percent iron.
 11. Thedie cast product of claim 8, wherein the die cast product comprises 0.45to 0.6 percent magnesium.
 12. The die cast product of claim 8, whereinthe one or more other elements is lead.
 13. The die cast product ofclaim 8, wherein the one or more other elements is chromium.
 14. The diecast product of claim 8, wherein the one or more other elements are leadand chromium.
 15. A method of making a die cast product by an SSM methodof casting, comprising: forming a semi-solid aluminum alloy, wherein thesemi-solid aluminum alloy comprises by percentage of weight: 6.5 to 8.5percent silicon; 0.6 to 1.0 percent iron; 0.0 to 0.5 percent manganese;0.35 to 0.65 percent magnesium; 0.0 to 1.0 percent zinc; 0.0 to 0.2percent titanium; 2.0 to 2.5 percent copper;  0.0 to 0.15 percent one ormore other elements; aluminum as the remainder; and placing the aluminumalloy in a die cavity.


16. The method of making the die cast product of claim 15, wherein theone or more other element is lead.
 17. The method of making the die castproduct of claim 15, wherein the one or more other element is chromium.18. The method of making the die cast product of claim 17, wherein theone or more other elements are lead and chromium.
 19. The method ofmaking the die cast product of claim 15, wherein the SSM method ofcasting is Rheocasting.
 20. The method of making the die cast product ofclaim 15, wherein the SSM method of casting is Thixocasting.